New European research has found that a woman's risk of miscarriage could be affected by her age, previous pregnancy history, and previous pregnancy complications.
Carried out by researchers at the Norwegian Institute of Public Health, the study used national health registers to gather information on all pregnancies in Norway between 2009 and 2013.
The researchers found that there was a total of 421,201 pregnancies during this time, and after accounting for induced abortions, the overall miscarriage rate was 12.8 percent.
A woman's risk of miscarriage was then estimated according to her age and pregnancy history.
The findings, published in The BMJ, showed that a woman's age appeared to affect her risk of miscarriage, with the risk lowest among women aged 25 to 29 (10 percent). It then increased rapidly after age 30, reaching 53 percent among women age 45 years and over.
Experiencing a previous miscarriage also increased the risk of experiencing another. After one miscarriage, the risk of another was increased by half, after two, the risk doubled, and after three consecutive miscarriages, the risk was four times greater.
Pregnancy complications including the previous birth ending in a preterm delivery, a cesarean section, or if the woman had diabetes during pregnancy, also modestly increased the risk of miscarriage.
The risk was also slightly higher for women who themselves had been born small.
However, pre-eclampsia in the previous pregnancy, which is abnormally high blood pressure, was not associated with increased risk of miscarriage.
Although miscarriage is common, the researchers note that it has been difficult to investigate what may influence miscarriage risk due to a lack of consistent data. Norway is one of the few countries where miscarriage data has been consistently recorded since 2008.
However, as the study is an observational one, the team note that they cannot establish cause and effect, although the findings do offer more precise estimates of the risk of miscarriage related to a mother's age, and suggest that previous pregnancy complications may also play a role.
"More focused studies of these associations might lead to new insights regarding the shared underlying causes of pregnancy complications and miscarriage," they conclude.